feat: sdk NoMemory/Cleaner + example build fixes

- sdk/plugin.go: ToolDef adds NoMemory/Cleaner fields
- sdk/plugin_test.go: unit tests for NoMemory/Cleaner
- all example plugins: NoMemory/Cleaner annotated for each tool
- plugindev/templates.go: template shows NoMemory/Cleaner pattern
- plugindev/cmd_build.go: fix ensureGoMod, buildBundle/buildTarget sdkPath param, NewPluginFactory
- example/go.mod: add external dependency declarations (chromedp, gofeed)
- add main.go stubs for all example plugins

sdk/plugin.go

@@ -92,6 +92,8 @@ type ToolDef struct {
 	Plugin      string                 `json:"plugin,omitempty"`
 	Description string                 `json:"description"`
 	Parameters  map[string]interface{} `json:"parameters"`
+	NoMemory    bool                   `json:"no_memory,omitempty"`  // 此工具输出不参与记忆计算，但原文保留
+	Cleaner     func(string) string    `json:"-"`                    // 计算层过滤函数，不改原文；仅在向量化/jieba/蒸馏时调用
 }
 
 // IOInjector provides methods for injecting input and interrupts into the agent pipeline.